Copper plays a key role in numerous environmentally and biologically important processes, particularly when encapsulated within enzymes that are widely distributed in Nature. The copper ions in the active sites of enzymes perform a variety of significant functions, including the binding and activation of dioxygen (O2) for effecting metabolically significant chemical reactions and the reduction of oxidized nitrogen-containing compounds like nitrite and nitrous oxide (N2O) during microbial respiratory processes important within the global nitrogen cycle. Despite extensive research, many questions remain unanswered concerning the detailed molecular level pathways of these processes. The research described herein addresses some of these questions through the synthetic modeling approach. In this approach, low molecular weight complexes designed to replicate aspects of copper enzyme active site structure and function are characterized and their reactivity studied. The goals are to develop detailed understanding of geometries, electronic structures, bonding, and reaction mechanisms relevant to the biological systems. In particular, the research aims to provide detailed understanding of the fundamental chemistry underlying the function of an important subset of copper-containing enzymes involved in the binding and activation of O2 and N2O. This objective will be addressed through three specific aims: (1) Dioxygen Activation at Monocopper Sites, (2) Dioxygen Activation at Multicopper Sites, and (3) Copper-Sulfur Chemistry for Modeling the CuZ Site of Nitrous Oxide Reductase. In aims (1) and (2), synthetic analogs of highly reactive mono- and multicopper oxidizing species will be prepared in order to evaluate their possible role in enzymes that bind and activate O2. In aim (3), new multicopper(I)-sulfide models of the unusual tetracopper-sulfide cluster (CuZ) found in an environmentally important enzyme, nitrous oxide reductase, will be synthesized and their reactivity with N2O will be studied. In addition to aspiring to a deep understanding of copper enzyme structure/function relationships, the proposed work is aimed at developing novel copper chemistry of fundamental significance. PUBLIC HEALTH RELEVANCE: The research aims to provide detailed understanding of the fundamental chemistry underlying the function of an important subset of copper-containing enzymes involved in the binding and activation of O2 and N2O. The dioxygen-activating enzymes are involved in a plethora of important biological processes central to life, including respiration, metal ion homeostasis (the disruption of which causes disease), and the production of important organic metabolites, hormones, and neurotransmitters essential to human health. The reduction of N2O by the microbial enzyme nitrous oxide reductase converts this greenhouse gas to inert N2 in a process recognized to be a critical component of the global nitrogen cycle and thus directly relevant to public health.